1. Field of the Invention
The invention relates to a method, apparatus and computer program for viewing on a client document data representing at least a part of a document to be printed.
2. Discussion of the Related Art
Most networks include a print server to which a print engine may be attached and a number of client computers sharing the resources of the print server so that the printer may be used by many users of the network. Documents to be printed may be sent from a client computer using a job submitter that transmits a print job from the client to the print server.
Documents to be printed usually contain text and graphics. Text describes letters and other symbols on a page, while graphics are for example a line, an illustration or a picture. Graphics may be transmitted to a print server as either an array of dots (bitmap graphics, also called raster graphics), or as a collection of lines (vector graphics). When an outline font is used, a letter is stored as a set of equations defining the lines which make the boundary of this letter.
The print server is provided with a controller having functions for the interpretation and rasterization. The interpretation function of the controller examines the data sent from the client computer and identifies the command embedded in the data, such as commands related to printer control, page format, font management, text layout and graphics. Rasterizing is the final stage in the process of preparing an image for printing, and converts the received commands into an array of dots to be used by the print engine. The print server is provided with a raster image processor (RIP) for performing the translation of a file containing vector format objects into a raster image file (also called bitmap file) to be sent to the print engine. Thus, the RIP produces the bitmap for each character of text, and places it at the specified position in the array and then overlays the array with any bitmap graphics, to form the pattern to be printed. Once the bitmap image file is ready, it is passed to the print engine.
A known method for viewing on a client computer the document data representing a document to be printed uses dedicated application software of the client. However this method requires proprietary client software and it has a number of drawbacks such as complexity and the fact that the view obtained on the client computer differs or deviates from the printed document. In particular, graphics and outline fonts are not rendered properly. Moreover the application software of the client has to be aware of all characteristics of all print engines accessible through the network. This requires very complex software that should be available on all client computers.
A method for viewing on a client computer the document data representing a document to be printed is known from European Patent Application Publication No. EP 1 132 808 A1. This publication describes how a print job is transmitted electronically to a reproduction center where it is converted into a format suitable for showing the final appearance of the printed document. The print job can be retransmitted in this format to the client for viewing purposes. The document obtained in this format, for example a PDF (Portable Document Format), is stored in a temporary document store of the reproduction center and then in a permanent document store of the reproduction center, and is then transmitted to the printer. This method, however, has the problem that the document converted for viewing purposes is print device independent and that only an approximate final appearance of the document to be printed can be obtained. Effects due to the print engine parameters (printer margins, paper size, positioning of image with respect to the paper, etc.) cannot be rendered properly. Moreover, outline fonts are not rendered accurately.